Paraventricular alpha1- and alpha2-adrenergic receptors mediate hindbrain lipoprivation-induced suppression of luteinizing hormone pulses in female rats

Acute central lipoprivation suppresses pulsatile luteinizing hormone (LH) release and increases blood glucose levels through noradrenergic input to the hypothalamic paraventricular nucleus (PVN) in female rats. The present study was conducted to identify adrenergic receptor subtypes involved in central lipoprivation-induced suppression of pulsatile LH secretion and increases in plasma glucose levels in female rats. Acute hindbrain lipoprivation was produced by injection into the fourth cerebroventricle (4V) of 2-mercaptoacetate (MA), an inhibitor of fatty acid oxidation, in estradiol-implanted ovariectomized rats. Two min before MA injection, alpha1-, alpha2- or beta-adrenergic receptor antagonist was injected into the PVN. Injection of MA into the 4V suppresses pulsatile LH release in PVN vehicle-treated rats, whereas pretreatment of animals with injection of alpha1- or alpha2-adrenergic antagonist into the PVN blocked the effect of the 4V MA injection on LH pulses. beta-Adrenergic antagonist did not affect MA-induced suppression of LH pulses. The counter-regulatory increase in plasma glucose levels after 4V MA injection was also partially blocked by pretreatment with alpha1- and alpha2-adrenergic receptor antagonists. These results suggest that alpha1- and alpha2-adrenergic receptors in the PVN mediate hindbrain lipoprivation-induced suppression of LH release and counter-regulatory increases in plasma glucose levels in female rats.     

植物甾醇对去卵巢KM小鼠血清生殖激素及乳腺组织孕激素受体的影响

本试验旨在研究植物甾醇对去卵巢小鼠血清激素及乳腺组织中孕激素受体的影响。50只雌性小鼠,随机选40只进行去卵巢手术,恢复7 d。分组如下：正常组、去卵巢对照组、植物甾醇低、中、高3个剂量组（每日灌胃20、80和320 mg/kg植物甾醇）。连续灌胃3周,第22天采集血样和乳腺组织,对小鼠血清中的雌二醇、孕酮和催乳素水平进行检测,对乳腺组织的孕激素受体基因表达进行荧光定量检测。结果表明,去卵巢对照组小鼠雌二醇水平显著低于正常组（P〈0.05）。植物甾醇组小鼠血清雌二醇水平持续升高,其中,高剂量组小鼠血清雌二醇水平与正常组最接近;与去卵巢对照组相比,去卵巢植物甾醇组小鼠血清孕酮水平均有提高,但差异不显著（P〉0.05）;与去卵巢对照组相比,去卵巢植物甾醇组小鼠催乳素水平先下降后上升,但他们之间无显著差异（P〉0.05）。与去卵巢对照组相比,植物甾醇各剂量组小鼠孕激素受体基因相对表达量呈上升趋势,低、中、高剂量组小鼠孕激素受体基因相对表达量分别是去卵巢对照组的1.05、1.13和2.78倍。植物甾醇可改善去卵巢小鼠内源激素不平衡的状况,促进乳腺组织PR基因的表达。     

Feedback of 17 beta-estradiol on secretion of luteinizing hormone during different seasons of the year

The working hypothesis was that the amount of increase in secretion of luteinizing hormone (LH) that results from positive feedback of 17 beta-estradiol (E2) is dependent on season of the year in mature bovine females. Seven beef cows, ovariectomized approximately 2 mo before the initiation of the experiment, were used in the initial year (1983) of the study. Three of the ovariectomized cows (OVX-E2) received an sc E2 implant, which provided low circulating levels of E2. The remaining four cows (OVX) were not implanted. Blood samples were collected serially (at 10-min intervals for 6 h) at each spring and fall equinox and at each summer and winter solstice. This protocol was replicated with a different group of cows in 1985 (OVX-E2, n = 4; OVX, n = 6). Concentration of LH in blood serum was quantified in all samples. Concentration of E2 in blood serum was measured in pools of samples from each serial blood collection. Concentrations of E2 were higher (P less than .05) in the implanted cows. Mean concentration of LH and amplitude of pulses of LH were higher (P less than .05) at each season of the year in cows that were ovariectomized and implanted with E2 than in cows that were ovariectomized and did not receive E2. An effect of season of the year on mean concentration of LH was detected (P less than .01). No influence of season or E2 was detected for frequency of pulses of LH. There was no significant treatment X season interaction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dexamethasone on gonadotrophin secretion in the gonadectomized sow and boar.

Saline solution or dexamethasone (DXM, 35 micrograms/kg bodyweight) was injected intramuscularly twice daily for four days into five ovariectomized sows and five castrated boars. Blood samples from an indwelling jugular vein catheter were taken at 15 min intervals for 12 h prior to DXM injection and on the fourth day of treatment in order to compare the effect on variables describing the pulsatile secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Dexamethasone treatment caused a decrease (p less than 0.05) in the number of pulsatile episodes of LH secretion in both gonadectomized boars and sows resulting in a significant decrease in mean concentrations. Follicle stimulating hormone secretion parameters appeared to be unaffected by DXM injection in both groups of animals. It is concluded that previously described differences in LH suppression in boars and sows given glucocorticoids may be attributed to the influence of gonadal hormones.     

Inhibin and reproduction. First communication: changes to inhibin level in Barki ewes after artificial infection with bluetongue virus

Bluetongue virus type 16, isolated from sheep in Egypt, was injected to 4 normally cycling Barki ewes and caused high levels of inhibin. This was assayed by a biological method, using suppression of the luteinising hormone (LH) of castrated rats. Albumin (fraction 2) was injected to normally cycling ewes. The sera of injected ewes were investigated 1 day after injection and weekly up to the 4th one injection. There was a gradual decrease of LH (4.8 +/- 0.52 I.U./ml serum) until the minimum level (1.17 +/- 0.25 I.U./ml serum) was reached, in comparison to the control serum LH which was 5.26 +/- 0.52 I.U./ml serum during the dioestrous phase.     

GnIH与INH表位多肽疫苗主动免疫对甘肃高山细毛羊生殖激素的影响

本试验通过合成促性腺激素类的抑制激素——抑制素(inhibit hormone,INH)与促性腺激素抑制激素(gonadotropin inhibiting hormone,GnIH)的INH表位多肽疫苗和GnIH表位多肽疫苗,主动免疫甘肃高山细毛羊并对促卵泡素(follicle stimulating hormone,FSH)和促黄体素(luteinizing hormone,LH)激素水平进行比较分析。试验选用15只处在非发情季节的3.5岁的甘肃高山细毛羊,注射INH表位多肽疫苗与GnIH表位多肽疫苗分别为表位多肽疫苗A组和表位多肽疫苗B组,对照组注射等量生理盐水。采血后进行免疫,每隔7 d免疫和采血,同时在发情后每隔15 min采集一次血液,分离血清,用ELISA试剂盒检测抗体水平及FSH和LH激素变化。结果表明,表位多肽疫苗A组和表位多肽疫苗B组在初次免疫后都产生了相应的抗体,且表位多肽疫苗B组较表位多肽疫苗A组产生的抗体浓度高,75 、90、105 min时,表位多肽疫苗B组相对表位多肽疫苗A组显著促进了FSH的分泌水平(P<0.05)。在45~105 min时,表位多肽疫苗B组相对表位多肽疫苗A组显著促进了LH的分泌水平(P<0.05),且在90到105 min时表位多肽疫苗A组和表位多肽疫苗B组血清中FSH和LH的水平均显著高于对照组(P<0.05)。本试验结果表明,INH表位多肽疫苗和GnIH表位多肽疫苗主动免疫促进了甘肃高山细毛羊的FSH、LH的分泌,GnIH表位多肽疫苗在甘肃高山细毛羊上具有更好的免疫作用,本研究为该表位多肽疫苗在绵羊上的运用奠定了基础。     

Effects of Active Immunization with GnIH and INH Epitope Peptide Vaccine on Reproductive Hormones of Gansu Alpine Fine-wool Sheep

This study aimed to detect the reproductive hormones levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in Gansu Alpine Fine-wool sheep by active immunization of two synthesized epitope peptide vaccines A and B which were combined inhibit hormone (INH) and gonadotropin inhibit hormone (GnIH).15 Gansu Alpine Fine-wool sheep were selected which were 3.5 year old and lived in anoestrus season, 3 groups each had 5 sheep, GnIH epitope peptide vaccine and INH epitope peptide vaccine were named epitope peptide vaccine A and B groups, while blank group was injected with saline.The blood was collected before immunization and immuned, and bloods were collected once every 7 days, meanwhile collected blood every 15 min after estrus.The serum was used to detect antibody, FSH and LH levels by ELISA Kits.The results showed that the epitope peptide vaccine A and B groups produced the corresponding antibodies after the initial immunization, and epitope peptide vaccine B group produced more antibodies than epitope peptide vaccine A group.Epitope peptide vaccine B group promoted the FSH secretion levels was significantly higher than epitope peptide vaccine A group in 75, 90 and 105 min (P<0.05);In 45 to 105 minutes, the LH secretion levels of epitope peptide vaccine B group was significantly higher than epitope peptide vaccine A group (P<0.05), while the LH and FSH levels in epitope peptide vaccine A and B groups were significantly higher than control group (P<0.05).This study indicated that the epitope peptide vaccine A and B groups could promote the FSH and LH secretion levels through active immunity in Gansu Alpine Fine-wool sheep and had a good immune function.This study laid a foundation for the application of epitope peptide vaccine on sheep.     

Associated luteinizing hormone-releasing hormone and luteinizing hormone secretion in ovariectomized gilts.

The secretion of luteinizing hormone-releasing hormone (LHRH) and its temporal association with pulses of luteinizing hormone (LH) was examined in ovariectomized prepuberal gilts. Push-pull cannulae (PPC) were implanted within the anterior pituitary gland and LHRH was quantified from 10 min (200 microliters) perfusate samples. Serum LH concentrations were determined from jugular vein blood obtained at the midpoint of perfusate collection. Initial studies without collection of blood samples, indicated that LHRH secretion in the ovariectomized gilt was pulsatile with pulses comprised of one to three samples. However, most pulses were probably of rapid onset and short duration, since they comprised only one sample. Greater LHRH pulse amplitudes were associated with PPC locations within medial regions of the anterior pituitary close to the median eminence. In studies which involved blood collection, LH secretion was not affected by push-pull perfusion of the anterior pituitary gland in most gilts, however, adaptation of pigs to the sampling procedures was essential for prolonged sampling. There was a close temporal relationship between perfusate LHRH pulses and serum LH pulses with LHRH pulses occurring coincident or one sample preceding serum LH pulses. There were occasional LHRH pulses without LH pulses and LH pulses without detectable LHRH pulses. These results provide direct evidence that pulsatile LHRH secretion is associated with pulsatile LH secretion in ovariectomized gilts. In addition, PPC perfusion of the anterior pituitary is a viable procedure for assessing hypothalamic hypophyseal neurohormone relationships.     

Luteinizing hormone, follicle stimulating hormone and prolactin secretion in ewes and wethers after zeranol or estradiol injection

Plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) were determined over a 24-h period using radioimmunoassay in sheep injected with corn oil (control) or various doses of zeranol or estradiol-17 beta. Injection of .333, 1 or 10 mg of zeranol caused dose-related increases (P less than .01) in plasma PRL (peak levels at 12 to 18 h) and LH (peak levels at 12 to 20 h) in ovariectomized ewes. Similarly, PRL and LH increased following doses of 33 or 100 microgram of estradiol. Before the LH surge, plasma LH levels were significantly depressed (4 to 8 h). Plasma FSH levels were significantly decreased 4 to 8 h after zeranol and estradiol injection. Slight surges of FSH were observed at times similar to those of LH, but the peak level was never greater than control levels. Injection of 1 mg of zeranol or 100 microgram of estradiol into wethers resulted in a 24-h pattern of PRL secretion not significantly different of LH concentration and significantly prolonged inhibition of FSH secretion. These results indicate similarities in the effects of zeranol and estradiol on anterior pituitary hormone secretion within groups of animals of the same sex or reproductive state. Differences in secretion and plasma concentrations of LH, FSH and PRL due to underlying sexual dimorphism are maintained and expressed even when animals are challenged with structurally different compounds of varying estrogenic potencies.     

Effects of 17 beta-estradiol and diets varying in energy on secretion of luteinizing hormone in beef heifers

An experiment was conducted to test the hypothesis that 17 beta-estradiol (E2) would not suppress secretion of luteinizing hormone (LH) in heifers fed a diet limited in energy during the period before the onset of nutritionally induced anestrus. Sixteen of 20 heifers that had been exhibiting normal estrous cycles (20 mo of age, 409 +/- 6 kg body weight) were ovariectomized, and half of them were assigned at random to receive an E2 implant. The ovariectomized heifers were assigned at random to receive diets that contained low (L; 5.8 Mcal X animal-1 X d-1, n = 8) or high levels of energy (H; 20.0 Mcal X animal-1 X d-1, n = 8) for 100 d. The other four heifers remained intact and were fed the L-diet. The intact heifers were utilized to determine the status of reproductive function in animals fed the L-diet. Heifers lost body weight rapidly after initiation of feeding the L-diet. Heifers fed the L-diet then stabilized at a lighter weight until the latter part of the experiment. One of the four intact heifers fed the L-diet became anestrus near the end of the study. Mean concentrations of LH in blood serum increased linearly (P less than .05) in ovariectomized heifers fed the L- and H-diet. Mean concentration of LH in heifers fed the H-diet that were implanted with E2 was similar to ovariectomized heifers fed the H-diet that received no E2. Mean LH in serum of ovariectomized heifers implanted with E2 fed the L-diet was suppressed and remained low throughout the study. Frequency of pulses of LH in ovariectomized heifers fed the L-diet was less (P less than .01) than that in ovariectomized heifers fed the H-diet. Estradiol decreased the number of pulses of LH in heifers fed the L-diet. We conclude that dietary energy restriction in beef heifers has a direct action on the hypothalamo-pituitary axis to lower the number of pulses of LH in the absence of ovarian steroids. However, ovarian E2 appears to suppress further secretion of LH in heifers fed limited levels of dietary energy before the onset of nutritional anestrus occurs, therefore, our working hypothesis is rejected.     

Effects of sodium pentobarbital on release of gonadotropins in ewes immediately after ovariectomy and after treatment with gonadotropin-releas ing hormone

Two experiments were conducted with ewes 9 to 11 days after estrus to determine whether the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are controlled differentially. In experiment 1, gonadotropin-releasing hormone (GnRH) was injected (100 (μg/ewe) at time = 0 min into ewes in four treatment groups. The treatment groups (9 ewes/group) were: 1) periodic iv sodium pentobarbital (NaPen) vehicle from 0 min; 2) periodic iv NaPen from 0 min; 3) vehicle iv for 120 min then iv NaPen from 120 min; 4) vehicle iv for 150 min then iv NaPen from 150 min. A surgical plane of anesthesia was maintained from the initiation of NaPen injection until the experiment ended. Jugular blood was sampled at 30-min intervals from ?30 to + 210 min for LH and FSH assays, and profiles of hormone concentrations were compared by time-trend analyses. GnRH released LH (P<.001) and FSH (P<.001), but NaPen did not affect the profiles of hormone concentrations; this indicated that NaPen did not reduce the ability of the pituitary to secrete gonadotropins in response to GnRH. Experiment 2 was a 2x2 factorial with ovariectomy (time = 0 hr) and NaPen as the main effects. One group of ovariectomized (n = 6) and one group of sham ovariectomized (n = 6) ewes were anesthetized only during surgery, while a group of ovariectomized (n = 7) and a group of sham ovariectomized (n = 6) ewes were kept at a surgical plane of anesthesia until 10 hr after surgery. Patterns of LH and FSH were compared in jugular blood collected hourly from 0 hr until 10 hr after surgery and in samples collected at 24 hr intervals from -24 to +72 hr of surgery. After ovariectomy, LH increased (P<.001) hourly and daily, but anesthesia suppressed (hourly, <.001 and daily, P<.005) these increases, which resulted in an interaction (hourly, P<.001 and daily, P<.01) of ovariectomy and anesthesia. FSH after ovariectomy increased hourly and daily (hourly, P<.02 and daily, P<.001), but the effect of anesthesia and interaction of ovariectomy and anesthesia were not significant. Because NaPen did not alter secretion of LH or FSH after exogenous GnRH in experiment 1 while it blocked the postovariectomy increase in LH but not FSH in experiment 2, we concluded that the postovariectomy increase in LH resulted from increased hypothalamic secretion of GnRH. The mechanisms responsible for the postovariectomy increase in FSH secretion are not identical to those for LH. The mechanisms that control the postovariectomy secretion of FSH might involve factors that are not suppressible by NaPen or, alternatively, the differences in LH and FSH release after ovariectomy might reflect the removal of ovarian factors that suppress FSH but not LH secretion in intact ewes.     

Luteinizing hormone secretion in hypophysial stalk-transected gilts given hydrocortisone acetate and pulsatile gonadotropin-releasing hormone.

The site within the hypothalamic-pituitary axis at which cortisol acts to inhibit luteinizing hormone (LH) secretion was investigated in female pigs. Six ovariectomized, hypophysial stalk-transected (HST) gilts were given 1 microgram pulses of gonadotropin releasing-hormone (GnRH) iv every 45 min from day 0 to 12. On days 6-12, each of 3 gilts received either hydrocortisone acetate (HCA; 3.2 mg/kg body weight) or oil vehicle im at 12-hr intervals. Four ovariectomized, pituitary stalk-intact gilts served as controls and received HCA and pulses of 3.5% sodium citrate. Jugular blood was sampled daily and every 15 min for 5 hr on days 5 and 12. Treatment with HCA decreased serum LH concentrations and LH pulse frequency in stalk-intact animals. In contrast, serum LH concentrations, as well as the frequency and amplitude of LH pulses, were unaffected by HCA in HST gilts and were similar to those observed in oil-treated HST gilts. We suggest that chronically elevated concentrations of circulating cortisol inhibit LH secretion in pigs by acting at the level of the hypothalamus.     

The effect of pulsatile gonadotropin-releasing hormone and estradiol administration on luteinizing hormone and follicle-stimulating hormone concentrations in pituitary stalk-sectioned ovariectomized pony mares

Hourly pulses of gonadotropin-releasing hormone (GnRH) or bi-daily injections of estradiol (E2) can increase luteinizing hormone (LH) secretion in ovariectomized, anestrous pony mares. However, the site (pituitary versus hypothalamus) of positive feedback of estradiol on gonadotropin secretion has not been described in mares. Thus, one of our objectives involved investigating the feedback of estradiol on the pituitary. The second objective consisted of determining if hourly pulses of GnRH could re-establish physiological LH and FSH concentrations after pituitary stalk-section (PSS), and the third objective was to describe the declining time trends of LH and FSH secretion after PSS. During summer months, ovariectomized pony mares were divided into three groups: Group 1 (control, n = 2), Group 2 (pulsatile GnRH (25 μg/hr), n = 3), and Group 3 (estradiol (5 mg/12 hr), n = 3). All mares were stalk-sectioned and treatment begun immediately after stalk-section. Blood samples were collected every 30 min for 8 h on the day before surgery (DO) and 5 d post surgery (D5) to facilitate the comparison of gonadotropin levels before and after pituitary stalk-section. Additionally, jugular blood samples were collected every 12 hr beginning the evening of surgery, allowing for evaluation of the gonadotropin secretory time trends over the 10 d of treatment. On Day 10, animals were euthanized to confirm pituitary stalk-section and to submit tissue for messenger RNA analysis (parallel study). Plasma samples were assayed for LH and FSH by RIA. Mean LH secretion decreased from Day 0 to Day 5 in Groups 1 and 3, whereas LH secretion tended (P < 0.08) to decrease in Group 2 mares. On Day 5, LH was higher (P < 0.01) in Group 2 (17.26 ± 3.68 ng/ml; LSMEANS ± SEM), than either Group 1 (2.65 ± 4.64 ng/ml) or group 3 (4.28 ± 3.68 ng/ml). Group 1 did not differ from Group 3 on Day 5 (P < 0.40). Similarly, mean FSH levels decreased in all groups after surgery, yet Group 2 mares had significantly (P < 0.001) higher FSH concentrations (17.66 ± 1.53 ng/ml) than Group 1 or Group 3 (8.34 ± 1.84 and 7.69 ± 1. 63 ng/ml, respectively). Regression analysis of bi-daily LH and FSH levels indicated that the time trends were not parallel. These findings indicate: 1) Pituitary stalk-section lowered LH and FSH to undetectable levels within 5 d after surgery, 2) pulsatile administration of GnRH (25 μg/hr) maintained LH and FSH secretion, although concentrations tended to be lower than on Day 0, and 3) E2 did not stimulate LH or FSH secretion.     

Possible role of histamine in the regulation of secretion of luteinizing hormone in the ewe

Concentrations of histamine were quantified by an enzymatic isotopic assay in different regions of the brain and pituitary gland of gonadal-intact and chronically ovariectomized ewes during the anestrous season. Sera concentrations of LH were confirmed to be elevated in ovariectomized compared with intact animals immediately before tissues were obtained. Areas of the brain that were examined included cerebral cortex, thalamus, pineal gland, hypothalamus (rostral, medial basal, median eminence), midbrain, cerebellum and brain stem. Concentrations of histamine were greatest within the thalamus, pineal gland, medial basal hypothalamus and median eminence. Histamine within the medial basal hypothalamus was greater (P less than .05) in ovariectomized than in ovarian-intact animals. Further experiments were designed to determine the effect of antihistaminic drugs on secretion of LH. Ovariectomized ewes were treated every 6 h (i.m.) for 24 h with diphenhydramine (an antagonist of the H1-receptor for histamine), cimetidine (an H2-receptor antagonist), a combination of the drugs, or vehicle. Twelve hours after initiation of treatments, animals were injected with estradiol. Diphenhydramine depressed (P less than .01) basal serum concentrations of LH and the positive feedback effect of estradiol on serum concentrations of LH. Cimetidine did not influence the pattern of secretion of LH. Diphenhydramine did not alter LHRH-induced release of LH in ovariectomized ewes or basal serum concentrations of LH in ovarian-intact anestrous ewes. We suggest that histamine acts at the level of the central nervous system through an H1-receptor mechanism to control secretion of LH in female sheep.     

Developmental hormonal profiles in rdw rats with congenital hypothyroidism accompanying increased testicular size and infertility in adulthood

Congenital hypothyroid mutant male rdw rats have enlarged testes in adulthood with dwarfism accompanied by infertility. To explain how rdw rats acquire enlarged testes in adulthood, we compared age-matched normal (N) rats at various developmental stages for blood levels of hormones, thyroxine (T4), follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T), and investigated whether T4 therapy (rdw+T4) from 3 weeks of age (w) until adulthood could induce recovery of fertility in rdw rats, as well as how rdw+T4 affected hormonal patterns. Testes weights of rdw rats were higher than those of N rats at 19 w in adulthood though it was low during development. Serum T4 values in rdw rats were markedly lower than those in N rats but steadily increased up to 19 w. The serum FSH values in rdw rats were lower than those in N rats at all ages, and neither serum LH nor T value was significantly different at any age. The testes weight of rdw+T4 rats was significantly higher than that of N rats at 13 w with recovered growth, and was higher than that of rdw rats at 19 w. When they were mated with proestrous females after 16 w, all females became pregnant and gave birth to a normal number of pups. The T4 and FSH values of rdw+T4 rats were significantly higher than those in rdw rats, but similar to those in N rats in adulthood. The results suggest that even low levels of circulating thyroid hormone (TH) in rdw rats stimulate the development of their testes, probably through Sertoli cells, resulting in the enlarged adult testes without fertility, and that a sufficient circulating TH level from the immature stage plays a pivotal role in restoring mating activity, probably through FSH-mediated action towards adulthood.     

A luteinizing hormone-releasing hormone-induced serum luteinizing hormone surge is not detectable in the milk of cows

Six lactating Holstein cows were used to determine whether a serum luteinizing hormone (LH) surge induced by luteinizing hormone-releasing hormone (LHRH) could be detected in milk. A double antibody radioimmunoassay was evaluated for measuring LH in whole milk. Cows (d 10 of the estrous cycle) were injected with saline (time zero), followed by LHRH 12 h later. Blood samples were collected hourly for 12 h via jugular cannula following each injection; milk removal was accomplished every 2 h by a portable milking machine. On d 10 of the next estrous cycle, treatment, order was switched, with the same cows receiving LHRH at time zero and saline 12 h later. Approximately 2 h following LHRH treatment, serum LH levels peaked at 29 ng/ml and remained elevated for 5 h. There was no corresponding change in milk LH detected during the 12-h to 24-h period following the induced serum LH surge. Our conclusion is that the measurement of LH in the milk of cows shows little promise for predicting ovulation time in the cow.     

Effect of furazolidone and nitrofurazone on egg production, on plasma luteinising hormone and on prolactin concentrations in turkeys

1. Furazolidone or nitrofurazone were given orally to laying turkeys at doses of 7.5, 15 or 30 mg/kg for 7 d. Plasma concentrations of luteinising hormone (LH), prolactin (PRL) and egg production were measured before, during and after treatment. 2. Both drugs produced dose-dependent decreases in LH concentration which were statistically significant at doses of 15 and 30 mg/kg. Plasma PRL concentration was significantly increased in birds receiving 15 or 30 mg/kg of nitrofurazone, and tended to increase in the other treated groups, but this was not statistically significant. 3. Egg production was lowered in a dose-dependent manner by both drugs. However, nitrofurazone appeared to be more potent in reducing egg production than furazolidone. 4. Birds given 15 mg/kg of either drug were injected intramuscularly with luteinising hormone releasing hormone (LHRH) at a dose of 5 micrograms/kg and blood was collected immediately before and 30 min after LHRH administration. 5. Nitrofurazone significantly reduced the rise in LH induced by LHRH. Seven days after withdrawing the drug, the LHRH-induced LH release was not significantly different when compared to that in the control group or that seen on day 7 of treatment.     

Involvement of neurokinin receptors in the control of pulsatile luteinizing hormone secretion in rats

It has recently been shown that neurokinin B, a tachykinin, is associated with GnRH pulse generation in sheep and goats. The aim of the present study was to clarify the role of tachykinin receptors in the control of LH secretion in rats. To this end, we evaluated the effect of CS-003, an antagonist for all three neurokinin receptors (NK1, NK2 and NK3 receptors), on pulsatile LH secretion in both sexes of rats with different routes of administration. Both oral and third ventricular administration of CS-003 suppressed LH secretion in both sexes of gonadectomized animals. Furthermore, intact male rats with oral administration of CS-003 showed decreased serum testosterone levels, which might be due to suppressed LH secretion. None of the three subtype-specific neurokinin receptor antagonists showed a significant effect on LH secretion in ovariectomized rats when each antagonist was singly administered. The present results suggest that neurokinins play a role in the control of pulsatile GnRH/LH secretion via multiple neurokinin receptors in both male and female rats.     

Effects of estradiol-17β, para-chlorophenylalanine and quipazine on tonic and LHRH-induced secretion of luteinizing hormone in ovariectomized ewes

Changes in metabolism of serotonin (5-HT) might mediate the reduced tonic luteinizing hormone (LH) and increased pituitary responsiveness to luteinizing hormone releasing hormone (LHRH) caused by estradiol-17β (estradiol). Two experiments were conducted to determine effects of estradiol, para-chlorophenylalanine (PCPA), an inhibitor of synthesis of 5-HT, and quipazine, an agonist of 5-HT, on tonic and LHRH-induced secretion of LH in ovariectomized ewes during the summer. Tonic levels of LH were reduced, the interval from LHRH to peak of the induced surge was longer and the magnitude of release of LH was greater in ovariectomized ewes treated with estradiol than in controls. Neither PCPA nor quipazine affected tonic secretion of LH. In ovariectomized ewes not receiving estradiol, PCPA and quipazine increased the magnitude of the LHRH-induced release of LH. However, PCPA reduced pituitary sensitivity to LHRH when administered concomitantly with estradiol; treatment with quipazine attenuated this effect of PCPA. The interval to the peak of the induced surge of LH was not affected by PCPA or quipazine in estradiol-treated or control ovariectomized ewes. Based on these results it appears that 5-HT mediates or is required for estradiol to increase pituitary responsiveness to LHRH.